The overall objective of the project is to determine the functions of two conserved cellular components, the Ro ribonucleoprotein particles (RNPs) and the La protein. These two cellular components are frequent targets of the autoimmune response in patients with systemic lupus erythematosus and Sjogren's syndrome. In addition, maternal anti-Ro and anti-La antibodies are highly associated with complete congenital heart block in neonates. The Ro RNPs consist of a 60 kilodalton protein (and possibly additional proteins) that bind one of several small RNA molecules of about 100 nucleotides in length. Although these particles appear to be components of all vertebrate cells, their subcellular location is controversial, and their function is unknown. A subset of the Ro RNPs also binds the La protein, a 50 kd phosphoprotein that binds all known RNA polymerase III transcripts early in their biogenesis. Although the La protein has been suggested to be required for transcription termination by RNA polymerase III, it is possible that this protein functions in some other aspect of the biogenesis of polymerase III RNAs. Like the Ro RNPs, the La protein has been detected in a wide variety of vertebrate cells. In addition, proteins with similar biochemical characteristics as the mammalian La protein have been detected in nematodes and yeast. The ubiquitous distribution and apparent conservation of the Ro RNPs and the La protein argue that they are important components of eukaryotic cells. The first aim of this proposal is to definitively determine the subcellular location of the Ro RNPs using antibodies and nucleic acid probes. The second objective is to identify molecules that interact with Ro RNPs using psoralen and UV-cross-linking and co-immunoprecipitation with anti-Ro antibodies. The third aim is to identify Ro RNPs and the La protein in organisms that will allow a genetic approach to function. The identification of homologues of the Ro RNPs and the La protein in either Drosophila, nematodes or yeast will allow us to assess the consequences of genetically depleting these components from cells and organisms and to genetically identify factors that interact with Ro RNPs and the La protein. Determination of the functions of these conserved cellular components will expand our knowledge of basic cellular processes and may also provide clues to why these particles are frequent targets of the immune response in certain autoimmune diseases.